Injection molding process parameters of common plastics

1、 High density polyethylene
(HDPE) barrel temperature feeding zone 30~50 ℃ (50 ℃)
Zone 1 160~250 ℃ (200 ℃)
Zone 2 200~300 ℃ (210 ℃)
Zone 3 220~300 ℃ (230 ℃)
Zone 4 220~300 ℃ (240 ℃)
Zone 5 220~300 ℃ (240 ℃)
Nozzle 220~300 ℃ (240 ℃)
The temperature in brackets is recommended as the basic setting value, the stroke utilization is 35% and 65%, and the ratio of module flow length to wall thickness is 50:1 to 100:1
Melt temperature 220~280 ℃
Constant temperature of material barrel 220 ℃
Mold temperature 20~60 ℃
The injection pressure has good flow performance, avoiding the use of excessive injection pressure of 80~140MPa (800~1400bar);
Except for some thin-walled packaging containers, which can reach 180MPa (1800bar), the degree of shrinkage is relatively high, and it takes a long time to maintain the pressure of the product. Dimensional accuracy is the key factor, which is about 30%~60% of the injection pressure
Back pressure 5~20MPa (50~200bar); Where the back pressure is too low, it is easy to cause uneven product weight and dispersion
Injection speed requires high injection speed for thin-walled packaging containers, and medium injection speed is often more suitable for other types of plastic products
High screw speed (linear speed 1.3m/s) is allowed, as long as the plasticizing process is completed before the end of cooling time; The torque requirement of screw is low
Metering stroke 0.5~4D (minimum~maximum); It is important that the measuring stroke of 4D provides enough residence time for the molten metal
The residual amount is 2~8mm, depending on the metering stroke and screw diameter
Pre-drying is not required; If the storage conditions are not good, it can be dried at 80 ℃ for 1h
The recovery rate can reach 100%
Shrinkage 1.2~2.5%; Easy to twist; High degree of shrinkage; No further shrinkage after 24h (shrinkage after molding)
Point gate of gate system; Heated hot runner, insulated hot runner, inner casting sleeve; The cross section area is relatively small, which is sufficient for thin section products
There is no need to use other materials for special cleaning during machine downtime; PE temperature rise resistance
Standard screw of barrel equipment, standard three-stage screw; For packaging container products, the geometric shape of mixing section and shear section is special (L: D=25:1), straight nozzle, check valve
2、 Polypropylene (PP)
Barrel temperature feeding zone 30~50 ℃ (50 ℃)
Zone 1 160~250 ℃ (200 ℃)
Zone 2 200~300 ℃ (220 ℃)
Zone 3 220~300 ℃ (240 ℃)
Zone 4 220~300 ℃ (240 ℃)
Zone 5 220~300 ℃ (240 ℃)
Nozzle 220~300 ℃ (240 ℃)
The temperature in brackets is recommended as the basic setting value, the stroke utilization is 35% and 65%, and the ratio of module flow length to wall thickness is 50:1 to 100:1
Melt temperature 220~280 ℃
Constant temperature of material barrel 220 ℃
Mold temperature 20~70 ℃
The injection pressure has good flow performance, avoiding the use of excessive injection pressure of 80~140MPa (800~1400bar);
Except for some thin-walled packaging containers, the pressure retaining pressure of 180MPa (1800bar) can be reached to avoid wall shrinkage of products, and it takes a long time to maintain the pressure of products (about 30% of the cycle time); About 30%~60% of injection pressure
Back pressure 5~20MPa (50~200bar)
Injection speed requires high injection speed (with accumulator) for thin-walled packaging containers; Medium injection speed is often more suitable for other types of plastic products. High screw speed (linear speed is 1.3m/s) is allowed, as long as the plasticizing process is completed before the end of cooling time
Metering stroke 0.5~4D (minimum~maximum); It is important that the measuring stroke of 4D provides enough residence time for the molten metal
The amount of residual material is 2~8mm, which depends on the metering stroke and screw speed and is not required for pre-drying; If the storage conditions are not good, it can be dried at 80 ℃ for 1h
The recovery rate can reach 100%
Shrinkage 1.2~2.5%; High degree of shrinkage; No further shrinkage after 24h (shrinkage after molding)
Point gate or multi-point gate of gate system; Heated hot runner, insulated hot runner, inner casting sleeve; The gate position is at the thickest point of the product, otherwise large shrinkage is likely to occur
There is no need to use other materials for special cleaning during machine downtime; PP temperature-resistant barrel equipment standard screw, standard three-stage screw; For packaging container products, the geometric shape of mixing section and shear section is special (L: D=25:1), straight nozzle, check valve
3、 Polystyrene (PS)
Barrel temperature feeding zone 30~50 ℃ (50 ℃)
Zone 1 160~250 ℃ (200 ℃) Zone 2 200~300 ℃ (210 ℃)
Zone 3 220~300 ℃ (230 ℃)
Zone 4 220~300 ℃ (230 ℃)
Zone 5 220~300 ℃ (230 ℃)
Nozzle 220~300 ℃ (230 ℃)
The temperature in brackets is recommended as the basic setting value. The stroke utilization ratio is 35% and 65%. The ratio of module flow length to wall thickness is 50:1 to 100:1. The melt temperature is 220~280 ℃
Constant temperature of material barrel 220 ℃
The injection pressure at the mold temperature of 15~50 ℃ has good flow performance. Avoid using too high injection pressure of 80~140MPa (800~1400bar) to maintain the pressure
30%~60% of injection pressure; Relatively short pressure holding time
Back pressure 5~10MPa (50~100bar); In places where the back pressure is too low, bubbles are easy to form in the molten material (there are gray and black lines in the products)
The injection speed is generally fast, and multi-level injection is based on the shape of the product; Thin-walled packaging containers should be as fast as possible. If necessary, it is allowed to use the accumulator screw with high screw speed (the maximum linear speed is 1.3m/s); However, in order to achieve good results, the plasticizing process should be slow as the cooling time
Metering stroke 0.5~4D (minimum~maximum); It is important that the measuring stroke of 4D provides enough residence time for the molten metal
The amount of residual material is 2~8mm, which depends on the metering stroke and screw speed and is not required for pre-drying; If the storage conditions are not good, it can be dried at 80 ℃ for 1h
The recovery rate can reach 100%
Shrinkage 0.3%~0.6%
Point gate of gate system; Heated hot runner, insulated hot runner, inner casting sleeve; The relatively small cross section is sufficient for machine downtime without special cleaning with other materials; PS temperature rise resistance
Barrel equipment standard screw, straight nozzle, check valve
4、 Polyvinyl chloride - unplasticized (PVC-U)
Barrel temperature feeding zone 30~50 ℃ (50 ℃)
Zone 1 140~160 ℃ (150 ℃)
Zone 2 165 ～ 180 ℃ (170 ℃)
Zone 3 180~210 ℃ (190 ℃)
Zone 4 180~210 ℃ (200 ℃)
Zone 5 180~210 ℃ (200 ℃)
Nozzle 180~210 ℃ (200 ℃)
The temperature in brackets is recommended as the basic setting value. The stroke utilization ratio is 35% and 65%. The ratio of module flow length to wall thickness is 50:1 to 100:1. The melting temperature is 210~220 ℃. The barrel temperature is 120 ℃
Mold temperature 30~60 ℃
Injection pressure 80~160MPa (800~1600bar)
The pressure retaining pressure cannot be set too high, 40~60% of the injection pressure, based on the mold and gate
In view of its thermal sensitivity, it is critical to set the back pressure correctly; The heat generated by screw rotation friction (close the heat input control) is better than the heat generated from the barrel heating ring; Back pressure shall not exceed 30MPa (300bar)
Do not set the injection speed too high and be careful of the shear effect of the material; Multi-stage injection speed is absolutely necessary where the product is prone to denaturation or sharp edges
The screw speed shall be the lowest setting allowed, and the maximum speed shall be converted into linear speed of 0.2m/s; If necessary, delay the plasticization to ensure that the metering operation can be completed before the end of the cooling time at low screw speed in the case of long cooling time; Requires high torque and maintains a uniform metering stroke of 1.0~3.5D
The residual amount should be small: 1~5mm, depending on the metering stroke and screw diameter; The screw ensures the minimum fit when installing the barrel
If the storage condition of pre-drying is not good, the recovery rate can be obtained after drying at 70 ℃ for 1h, and the material can be recycled without thermal decomposition
The shrinkage rate is 0.5%~0.7%, the gate system is straight gate, and the slice gate or round gate is better, and the point gate can also be used for small products; The gate should have an arc transition towards the direction of the product
Turn off the heating during the shutdown period of the machine, plasticize without back pressure, allow the molten material to flow for 2~3mm, and then operate the machine slowly like an extruder; Repeat the operation until the barrel temperature drops to 160 ℃, then extrude the remaining material and empty the barrel
Rigid PVC screw of barrel equipment; Some materials need to be provided with heating coil and cold air blowing device; Screw head with or without screw groove, straight through nozzle
5、 Plasticized polyvinyl chloride (P-PVC)
Barrel temperature feeding zone 30~50 ℃ (50 ℃)
Zone 1 140~160 ℃ (150 ℃)
Zone 2 150 ～ 180 ℃ (165 ℃)
Zone 3 160~220 ℃ (180 ℃)
Zone 4 160~220 ℃ (190 ℃) Zone 5 160~220 ℃ (190 ℃)
Nozzle 160~220 ℃ (200 ℃)
The temperature in brackets is recommended as the basic setting value, the stroke utilization is 35% and 65%, and the ratio of module flow length to wall thickness is 50:1 to 100:1
Melt temperature 200~220 ℃, constant temperature of barrel 120 ℃
Mold temperature 30~50 ℃
Injection pressure 80~120MPa (800~1200bar)
30%~60% of injection pressure
Back pressure 5~10MPa (50~100bar)
Injection speed In order to obtain good surface quality, the injection should not be too fast (if necessary, use multistage injection). The screw speed should be set to medium screw speed, and the maximum converted linear speed is 0.5m/s
The metering stroke is 1.0~3.5D, and the residual volume is 2~6mm, depending on the metering stroke and screw diameter
Pre-drying is not required; Only when the storage conditions are poor, it can be dried at 70 ℃ for 1h
The recovery rate allows the material to be recycled without thermal decomposition
Shrinkage rate 1% ～ 2.5%
The gate system can use point gate for small products; There should be an arc transition in the direction of the gate towards the product. The machine should shut down the heating during shutdown, plasticize without back pressure, and operate several extrusion cycles
Barrel equipment standard screw, check ring, straight nozzle
6、 Nylon 6 (PA6)
Barrel temperature feeding zone 60~90 ℃ (70 ℃)
Zone 1 230~240 ℃ (240 ℃)
Zone 2 230~240 ℃ (240 ℃)
Zone 3 240~250 ℃ (250 ℃)
Zone 4 240~250 ℃ (250 ℃)
Zone 5 240~250 ℃ (250 ℃)
Nozzle 230~240 ℃ (250 ℃)
The temperature in brackets is recommended as the basic setting value, the stroke utilization is 35% and 65%, and the ratio of module flow length to wall thickness is 50:1 to 100:1
The temperature of feeding zone and zone 1 directly affects the feeding efficiency. Increasing these temperatures can make the feeding more average
Melt temperature 240~250 ℃
Constant temperature of material barrel 220 ℃
Mold temperature 60~100 ℃
The injection pressure is 100~160MPa (1000~1600bar). If it is to process thin section long runner products (such as wire ties), it needs to reach 180MPa (1800bar)
50% of injection pressure; Due to the relatively fast condensation of the material, a short holding time is sufficient. Reduce the pressure retaining pressure to reduce the internal stress of the product
The back pressure is 2~8MPa (20~80bar), which needs to be adjusted accurately, because too high back pressure will cause uneven plasticizing injection speed. It is recommended to use relatively fast
Injection speed; The mold has good ventilation, otherwise the product is prone to coking
Screw speed Screw speed is high, linear speed is 1m/s; However, it is better to set the screw speed lower, as long as the plasticizing process can be completed before the end of the cooling time; Lower screw torque required
Metering stroke 0.5 ～ 3.5D
The residual amount is 2~6mm, depending on the metering stroke and screw diameter
Pre-drying: drying at 80 ℃ for 4h, except feeding directly from the loading container; Nylon has water absorption, and should be stored in moisture-proof containers and closed hoppers; If the water content exceeds 0.25%, it will cause molding change
The recovery rate can be added by 10%
Shrinkage rate of return material: 0.7%~2.0%; Or add 30% glass fiber and the shrinkage is 0.3%~0.8%; If the temperature provided exceeds 60 ℃, the product shall be gradually cooled; Gradual cooling can reduce the shrinkage after molding, that is, the product shows better dimensional stability and small internal stress; Steam method is recommended; Nylon products can be checked for stress by welding flux
The gate system can be point type, latent type, slice type and straight gate; It is recommended to use blind holes and gate pits to cut off cold material points;
Hot runner can be used; Due to the narrow machinability temperature range of molten metal, the hot runner shall provide closed-loop temperature control